Synthesis,structure, and properties of 1,3-oxazacycloalkanes (review)

Research dealing with methods for the synthesis of 1,3-oxazacycloalkanes and their structures and homolytic and heterolytic transformations is reviewed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 435–449, April, 1982.     

Character of the products of bromination of 1,3-dioxacyclanes with N-bromosuccinimide

The dependence of the character and composition of the products of the reaction of equimolar amounts of N-bromosuccinimide and 1,3-dioxacyclanes on the ring size and the character of the substituent in the 2 position of the 1,3-dioxacyclane ring was examined. Reasons for the primary formation of bromination products of different types for five-, six-, and seven-membered cyclic acetals are proposed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 174–175, February, 1981.     

Synthesis of 1,3-dioxacyclan-2-yl-substituted 1,2,3-triazoles

A new method for preparing 4-(1,3-dioxacyclan-2-yl)-5-phenyl-1,2,3-triazoles in 30–75% yields has been developed on the basis of azide–alkyne cycloaddition to 2-phenylethinyl-1,3-dioxacyclanes. It has been shown that the best results are achieved when the reaction is carried out at 150–155°C in DMSO.     

REACTIONS OF 1,3-DIOXACYCLANES WITH SULPHURY COMPOUNDS

Abstract

Saturated 1,3-dioxacyclanes under acid catalysis conditions react with thiods forming thioacetals and glycols. The effect of the type of catalysts, structure of reagents and regime parameters on the direaction and selectivity of the process was studies.     

Kinetics and mechanism of the initiated oxidation of a number of 1,3-dioxacyclanes

The initiated oxidation of a number of cyclic acetals at 50–95°C was studied by kinetic methods. It was found that the examined 1,3-dioxacyclanes are oxidized via a free-radical mechanism with quadratic termination of the chains in the peroxide radicals. The strengths of the carbon-hydrogen bonds undergoing attack by the peroxide radicals range from 80 to 90 kcal/mole.     

Transformations of Cyclic Acetals under the Action of Some Organic and Inorganic Oxidants

Liquid-phase oxidation of cyclic acetals and 2,2-disubstituted 1,3-dioxacyclanes with dimethyldioxirane, Caro salt, potassium persulfate, and complex of potassium chlorodiperoxochromate with 15-crown-5 was studied.     

Selective functionalization of the primary hydroxy group in triols

A procedure was suggested for preparing functionally substituted 1,2-diols by O-alkylation of hydroxyalkyl-1,3-dioxacyclanes with alkyl halides, followed by acid hydrolysis. The conditions for selective cleavage of the ethers obtained were found. (2,2-Dimethyl-1,3-dioxolan-4-yl)methyl benzoate under the conditions of acid deacetalization undergoes saponification of the ester group.     

Investigation in the Area of Furan Acetal Compounds. 13. Synthesis and Structure of 1,3-Dioxacyclanes Based on Furfural and Glycerol

The optimum conditions were found for the condensation of glycerol with furfural. It was shown that the reaction of glycerol with furfural gives a mixture of the cis and trans isomers of five- and six-membered furan 1,3-dioxacyclanes. The cis- and trans-5-hydroxy-2-furyl-1,3-dioxanes were isolated by column chromatography, and their stereochemical structure was established by IR and NMR spectroscopy.     

The liquid-phase free radical isomerization of cyclic dimethylformamide acetals

In the presence of tert-butyl peroxide, 2-dimethylamino-1,3-dioxacyclanes are converted to esters of dimethylcarbamic acid. The reaction is described by a kinetic equation for an unbranched chain reaction with quadratic chain termination. The five-membered heterocycle is more reactive than the six-membered heterocycle. The predominant site for free radical attack is the methine group adjacent to the three heteroatoms.     

Homolytic addition of 1,3-oxathiolane to unsaturated hydrocarbons

The homolytic addition of 1,3-oxathiolane to olefins takes place with the formation of 2-substituted 1,3-oxathiolanes and insignificant amounts of functional derivatives of sulfides.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 259–263, February, 1986.     

Novel Free Radical Reactions in Organosulfur Chemistry

Abstract

Our studies on homolytic and oxidative transformations of organic compounds of biand hexavalent sulfur cover mainly the following trends:     

Thermal decomposition of branched silanes: a computational study on mechanisms

The initial steps of the thermal decomposition of silanes in the gas phase were examined by DFT-B3LYP calculations, with particular attention being paid to the way in which the reactivity pattern changes with the degree of branching of the silane. Besides the established pathways-1,2-hydrogen shift, H(2) elimination, and homolytic dissociation-1,3-hydrogen shift was also explored as an initial reaction step which leads to disilene structures. Subsequent silylene insertion and initial steps of radical chain reactions were also studied. To estimate the energetic changes with temperature, various reaction free energies and the corresponding activation free energies up to 650?°C were calculated. Accordingly, the leading reaction channel at room temperature is 1,2-hydrogen shift with subsequent silylene insertion; for higher degrees of branching, competing pathways (homolytic dissociation, 1,3-hydrogen shift, and radical polymerization) gain in relative importance. At high temperatures, the rate-determining step changes to homolytic dissociation, and thereby the apparent rates of decomposition become dependent on the degree of branching.     

Homolytic reactions of dithiols with alkynes: A method of synthesis of 1,3- and 1,4-dithiacycloalkanes

The homolytic addition of alkanedithiols to alkynes gives 5–7-membered 1,3- or 1,4-dithiacycloalkanes, depending on the structures of the componentsTranslated from Izvestiya Akademii Nauk SSSR, Seriya Khimcheskaya, No. 12, pp. 2801–2810, December, 1990.     

Etude du Comportement Photochimique de quelques Diaryl-1,3-triazènes

Study of the Photochemical Behaviour of Some Diaryl-1,3-triazenes The photolysis of Diaryl-1,3-triazenes gives products whose structures are consistent with a cage recombination process of homolytically formed radicals and subsequent abstraction of hydrogen from the solvent molecules by arylamino radicals. In aromatic solvents, a free-radical chain process leads to the formation of products resulting from the homolytic substitution on the solvent. Quenching experiments show that singlet and triplet excited states are reactive but that intersystem crossing efficiency is low.     

Homolytic telomerization of vinyltrimethylsilane with 5,5-dimethyl-1,3-dioxane

The homolytic telomerization of vinyltrimethylsilane by 5,5-dimethyl-1,3-dioxane follows three principal routes, with the formation of 2- and 4-substituted 5,5-dimethyl-1, 3-dioxanes and a formate ester. The rings in the reaction products (2-trimethylsilylethyl- and 4-trimethylsilylethyl-5,5-dimethyl-1,3-dioxane) exist in the chair conformation. The substituants in the 2- and 4-positions of the dioxane ring occupy equatorial positions.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1031–1035, August, 1986.     

Homolytic addition of polyhaloalkanes to α-vinyloxy-ω-trialkylstannoxy-alkanes as a new route to 2-perhaloalkylmethyl-substituted 1,3-dioxacyclanes

Photoinduced reactions of -vinyloxy--trialkylstannoxyalkanes, CH₂=CHO(CH₂) _n OSnEt₃ (n = 2 to 4), with polyhaloalkanes result in 2-perhaloalkylmethyl-substituted 1,3-dioxacyclanes.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1824–1826, September, 1995.     

Bulky Substituent Effect on Reactivity of Localized Singlet Cyclopentane‐1,3‐diyls with π‐Single Bonding (C‐π‐C) Character

Thorough investigation of key intermediates, such as long‐lived singlet diradicals, is essential to understand the homolytic bond cleavage reactions. In this study, we evaluate the effect of bulky substituents at the meta‐position of the phenyl ring on the bond formation process in singlet 2,2‐diethoxy‐1,3‐diarylcyclopentane‐1,3‐diyls. The bulky groups have significant influence on the diradical lifetime, as such, when the triisopropylphenyl group was used, the lifetime was 45 times longer than that of the parent diradical in benzene at 293 K.     

The photochemical behaviour of bis aryl-1,3 triazenes

The photolysis of bis aryl-1,3 triazenes carried out in non-aromatic solvents gives products whose structures are consistent with a cage recombination process of homolytically formed radicals and the subsequent abstraction of hydrogen from the solvent molecules by these arylamino radicals.In aromatic solvents, a free-radical chain process leads to the formation of products resulting from the homolytic substitution on the solvent.     

The chemistry of localized singlet 1,3-diradicals (biradicals): from putative intermediates to persistent species and unusual molecules with a π-single bonded character

Localized singlet diradicals (biradicals) are key intermediates in chemical reactions involving homolytic bond-cleavage and formation processes. The molecular structure and electronic structure had been historically elusive due to the short-lived character of the reactive intermediates. In the last 15 years, a significant development of singlet diradical chemistry was achieved after the pioneering findings of long-lived singlet diradicals. In this tutorial review, the recent development of localized singlet diradical chemistry is summarized and discussed. The following subjects are included (a) the mechanism by which the ground state spin-multiplicity of localized 1,3-diradicals is controlled; (b) the substituent and heteroatom effect on the most stable electronic configuration of the singlet 1,3-diradicals, type-1 versus type-2; (c) the molecular design for the long-lived singlet ground state diradicals; (d) the generation and characterization of the singlet diradicals; and (e) the future prospects.     

Radical [1,3] Rearrangements of Breslow Intermediates

Breslow intermediates that bear radical‐stabilizing N substituents, such as benzyl, cinnamyl, and diarylmethyl, undergo facile homolytic C? N bond scission under mild conditions to give products of formal [1,3] rearrangement rather than benzoin condensation. EPR experiments and computational analysis support a radical‐based mechanism. Implications for thiamine‐based enzymes are discussed.